Mixed SiO4-PO4 Cathodes for Higher-Energy Lithium-Ion Batteries
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Solution Overview
Problem
Lithium-ion batteries, particularly those using lithium iron phosphate (LFP) cathodes, face limitations in gravimetric energy density due to low discharge voltage and moderate capacity, necessitating the development of new cathode materials with improved properties for enhanced energy storage in applications like electric vehicles.
Innovation Solution
The use of lithium metal polyanion compounds with a mixture of SiO4 and PO4 anions, optimized through a machine learning-assisted design and experimental approach, to increase gravimetric energy density and cycling performance by adjusting stoichiometry and synthesis conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium iron phosphate (LFP) cathode materials are used, then low cost and high intrinsic safety are achieved, but limited energy density and low discharge voltage occur
Solution Approach 1:
The patent applies composite materials by combining LiMPO4 and Li2MSiO4 in a single cathode structure with a mixed anion system containing both PO4 and SiO4. This composite approach enables the material to simultaneously achieve high discharge voltage (inheriting from LiMPO4) and high capacity (inheriting from Li2MSiO4), resolving the energy density limitation of conventional LFP while maintaining safety benefits
Solution Approach 2:
The patent changes the chemical composition parameters by introducing a mixed anion system with specific ratios of PO4 and SiO4 (where 0 < x < 1 in the formula Li2-xM(PO4)y(SiO4)1-y). This parameter modification allows tuning of both voltage and capacity characteristics, achieving enhanced energy density while maintaining structural stability and safety
2Use of energy by moving object
If lithium-metal-phosphates (LMP) are used as cathode materials, then higher gravimetric energy density is achieved compared to LFP, but poor kinetics and lithium utilization occur due to two-phase interface orientation blocking Li-ion diffusion
Solution Approach 1:
The patent changes the compositional parameters by incorporating SiO4 units into the crystal structure, which modifies the phase transition behavior and interface orientation. This parameter change eliminates the blocking effect on Li-ion diffusion channels while preserving the high voltage characteristics of LMP, thereby improving lithium utilization without sacrificing energy density
Solution Approach 2:
The patent applies local quality by creating a mixed anion environment where PO4 and SiO4 units are distributed throughout the crystal structure. The SiO4 units locally modify the crystallographic orientation and phase interface characteristics, improving Li-ion diffusion pathways in specific regions while maintaining overall high energy density
Data Source
AI summary
The present technology discloses lithium metal polyanion (LMX) cathode compounds which contain a mixture of SiO4 and PO4 anions. Compounds based on silicate SiO4 anions can exhibit significantly higher gravimetric capacities than conventional lithium iron phosphate (LFP) materials. The present technology offers electrochemical advantages of the LMX compounds over compounds fabricated with only SiO4 anions. Machine learning can be used to provide the synthesis conditions and the stoichiometry of LMX compounds to maximize the gravimetric energy density of a battery cell.